1. Field of the Invention
This invention relates to an extended nip press apparatus for pressing water from a formed web. More particularly, the present invention relates to an extended nip press apparatus which includes a deflection compensating backing roll which supplies the force necessary to urge the backing roll and the elongate press shoe towards each other for pressing a web extending therethrough.
2. Information Disclosure Statement
With the introduction of the extended nip press, the amount of water removed from the formed web during the pressing operation was greatly increased when compared with the more conventional nipping techniques incorporating a pair of counter-rotating rolls.
The extended nip press includes essentially an elongate pressing shoe defining a concave surface which is pressed into close conformity with a backing roll thereby defining therebetween an elongate pressing nip. A press blanket extends through the extended nip with the blanket moving through the extended nip and relative to the elongate pressing shoe. The press blanket is lubricated on the inner surface thereof so that the blanket slides over the shoe and through the extended nip. Typically, one or more press felts extend through the extended nip. Such press felts extend through the extended nip between the press blanket and the backing roll with the formed web being disposed between the press felts.
Because of the high pressures involved and the extended dwell time of the formed web within the extended press nip, an improved water removing capability is achieved with the extended nip press compared with the more conventional press nips.
However, in the prior art, the press shoe is usually hydraulically urged towards the press blanket. One prior art extended nip press includes a piston which slides relative to a cylinder controllably connected to a source of hydraulic pressure such that on application of hydraulic pressure, the piston or elongate press shoe is urged into conformity with the backing roll. However, such pistons require relatively complex sealing means and are difficult to seal, particularly when a plurality of such pistons are provided along the cross-machine direction.
Another type of extended nip press includes a hydraulically urged piston which is connected to the elongate shoe by means of an elongate rod extending in a cross-machine direction thereby permitting the shoe to pivot relative to the piston.
A third means of urging the press blanket into close conformity with the backing roll includes the provision of hydrostatic bearing means whereby hydraulic pressure is applied directly to the press blanket. The edges of the press blanket are sealed in order to maintain hydrostatic pressure against the press blanket.
All of the aforementioned techniques are relatively complex and typically it is necessary to provide a backup extended nip press arrangement so that in the event of sealing failure, the backup arrangement can be brought into operation so that production is not unduly affected.
Such backup equipment is expensive and relatively difficult to install. The present invention seeks to overcome the aforementioned problem by eliminating the aforementioned relatively complex seal arrangements by using the hydraulic pressure exerted by means of a deflection compensated backing roll for providing the necessary pressing force for urging the backing roll into close conformity with the elongate pressing shoe.
Therefore, it is a primary object of the present invention to provide an extended nip press apparatus which overcomes the aforementioned inadequacies of the prior art devices and which makes a considerable contribution to the art of pressing water from a formed web.
Another object of the present invention is the provision of an elongate press shoe which is pivotally supported directly to a press frame and of providing a backing roll including a roll shell deflection compensating means for urging the roll shell towards the elongate shoe and for compensating for deflection of the roll shell relative to the shoe during passage of the web through the extended nip.
Another object of the present invention is the provision of an extended nip press apparatus in which the frame defines an elongate groove, the apparatus also includes a rod which extends in a cross-machine direction with the rod being partially disposed within the elongate groove and the shoe defines a further groove for the partial reception therein of the rod so that the shoe is permitted to pivot relative to the frame.
Another object of the present invention is the provision of an extended nip press apparatus in which the shell deflection compensating means includes a plurality of hydrostatic bearings which are disposed between the shell and a beam in a cross-machine direction for urging the shell into conformity with the elongate shoe.
Another object of the present invention is the provision of an extended nip apparatus in which each of the plurality of roll shell deflection compensating means includes a cylinder defined by the beam, the cylinder being controllably connected to a source of hydraulic pressure and a piston slidably cooperating within the cylinder such that when the cylinder is connected to the source of hydraulic pressure, the piston is urged towards the elongate shoe such that the roll shell is urged into conformity with the elongate shoe for pressing water from the web extending through the extended nip.
Other objects and advantages of the present invention will be apparent to those skilled in the art by consideration of the detailed description taken in conjunction with the annexed drawings.